Ondetti et al. in U.S. Pat. Nos. 4,046,889 and 4,105,776 disclose compounds which are useful as inhibitors of angiotensin converting enzyme and can be utilized to reduce blood pressure. Among the compounds disclosed by Ondetti et al. are L-proline derivatives of the formula ##STR2## wherein n can be zero or one; R can be hydroxy; R.sub.1 and R.sub.4 can be hydrogen or lower alkyl; R.sub.2 can be hydrogen, lower alkanoyl, or benzoyl; and R.sub.3 can be hydrogen, hydroxy, or lower alkyl.